April 17, 1885.] 



SCIENCE 



307 



The digestion experiments offer nothing of special 

 interest in this connection, and we pass at once to the 

 experiments upon the nutritive value of the digested 

 cellulose. These were so arranged as to compare the 

 effect of the latter with that of an equal weight of 

 sugar in two respects: 1°, as to its influence upon the 

 proteid metabolism of the body; and, 2°, as to its in- 

 fluence upon the gain or loss of fat. 



The influence of carbhydrates in the food, as is 

 well known, is to decrease the proteid metabolism, 

 as is shown by the diminished excretion of nitrogen 

 in the urine. In v. Knieriem's experiments, 22 grams 

 of crude fibre, of which 11.02 grams were digested, 

 decreased the proteid metabolism by 22%, while 11 

 grams of cane-sugar decreased it 15.3%: in other 

 words, the digestible crude fibre showed itself more 

 effective in this respect than an equal weight of 

 sugar. 



As regards the gain or loss of fat, the advantage is 

 on the side of the sugar; the latter diminishing the 

 daily loss from the body by 2.5 grams, while the cell- 

 ulose decreased it by 1.7 grams. 



These are the results of a single experiment, and, 

 as regards exact numerical values, are of course sub- 

 ject to correction by future investigations. They 

 certainly show, however, that the nutritive value of 

 cellulose is by no means insignificant, and probably 

 not very much below that of other carbhydrates. 

 If, as in the former article, we assume that the heat 

 evolved by the fermentation of the cellulose in the 

 alimentary canal is of use to the organism, then the 

 sole loss by the fermentation is the latent energy 

 carried off in the marsh-gas evolved. In that paper 

 the amount of that loss was estimated on the basis 

 of Henneberg and Stohmann's determinations of the 

 amount of marsh-gas excreted in their respiration ex- 

 periments. If, instead of this, the amount of marsh- 

 gas evolved in the fermentation of one gram of cellu- 

 lose be made the basis of the calculation, a somewhat 

 lower value for the cellulose results. According to 

 Tappeiner, one gram of cellulose yields 0.335 grams 

 C0 2 , 0.047 grams CH 4 , and 0.618 grams of organic 

 acids. One gram of cellulose yields 4,452 cal. ; 0.047 

 grams CH 4 , 614 cal. : leaving 3,838 cal. to represent 

 the available heat-value of the cellulose. One gram 

 of cane-sugar yields 4,173 cal. ; one gram of starch, 

 4,479 cal. : consequently, if our fundamental assump- 

 tion is correct, the value of one gram of cellulose is 

 about 92 % of that of cane-sugar, and about 86 % of 

 that of starch. These results agree well with those 

 of v. Knieriem's experiments; and the two together 

 appear to justify the conclusion, previously stated, 

 that the nutritive value of cellulose is not greatly 

 inferior to that of other carbhydrates. 



H. P. Armsby. 



The naval observatory publications. 



Referring to your criticism in Science for April 3, 

 on the delay in printing annual volumes of 'Astro- 

 nomical and meteorological observations' made at the 

 U. S. naval observatory, I am glad to be able to say 

 that the cause for complaint in this direction has 

 been, at least temporarily, removed; and in future 

 we hope to have our volumes printed as fast as the 

 limited number of computers will permit the proof- 

 sheets to be sent to the printer. 



During the closing days of congress, the following 

 resolution was introduced and concurred in: "That 

 the annual volume of the 'Astronomical and meteoro- 

 logical observations ' of the naval observatory for the 

 years 1881 and 1882 be printed, and that 2,000 addi- 

 tional copies of each volume be printed, of which 400 



copies will be for the use of the senate, 800 for the 

 use of the house, and 800 for the use of the navy 

 department, or for sale at the cost of paper and 

 printing." 



The manuscript sheets of the volume for 1881 are 

 now in the hands of the printer, to be followed im- 

 mediately by those for 1882; so that both of these 

 volumes will be distributed this year, and it is hoped 

 that we will continue to be able to have (as you very 

 pertinently suggest) all annual volumes printed in- 

 dependently of the regular appropriation for the navy 

 department. Allan D. Brown, 



Commander, U. S. navy. 

 U. S. naval observatory, "Washington, D.C., 

 April 6. 



An attempt to photograph the corona. 



Mr. Pickering's interesting experiments described 

 in Science for April 3 would seem to be practically 

 conclusive as to the unreality of the coronal forms 

 which appear upon the plates of Dr. Huggins and 

 Mr. Woods, if it were evident that he had observed 

 all the conditions which they indicate as essential. 



His letter, however, is silent in respect to one im- 

 portant point. It is not stated whether or not the 

 plates were ' backed ' with any light-absorbing sub- 

 stance, in order to prevent the so-called ' halation ' 

 produced by reflection from the back surface of the 

 plate under a strong light. The English observers 

 insist urgently upon the necessity of this precaution, 

 and use for the purpose, I believe, a coat of asphalt 

 varnish, colored with Brunswick black. It is possible 

 that even this expedient would not wholly prevent a 

 streaky scattering of light at the edge of the sun's 

 image, because minute particles of foreign matter 

 embedded in the glass itself would have their in- 

 fluence; but it is obvious, that, if the experiment was 

 tried without the precaution, it cannot be looked 

 upon as any way decisive. 



Perhaps Mr. Pickering would kindly supplement 

 his communication by a brief statement regarding 

 this point. C. A. Young. 



Princeton, N.J., April 8. 



In reply to Professor Young's communication, I 

 would say that the precaution to which he refers 

 was carefully attended to, and that all the plates 

 employed were backed the day before the eclipse with 

 asphalt varnish. It would be very interesting to 

 know how far the corona, as photographed by Dr. 

 Huggins, extends from the sun: for a very long ex- 

 posure would probably mask the real phenomenon; 

 one that was very short would be insufficient to 

 obtain an impression of it. My exposures were so 

 timed, that, by a long development, the darkening 

 could be traced to a distance of .8 of the sun's diam- 

 eter, while, with a short development, the darkening 

 only reached to .2. But in no case could any par- 

 ticular rays be identified in the different photographs. 



Wm. H. Pickering. 



Sir William Thomson's Molecular dynamics. 



As it is possible that some of your readers may 

 have obtained copies of the papyrograph report of 

 my lectures on molecular dynamics, delivered at Bal- 

 timore during October, 1884, I should be obliged by 

 your giving publicity to the following corrections: — 



P. 34, lines 18 and 19, delete ' We may call it a 

 dynamax but not a paradox.' I have no recollec- 

 tion of, nor can I imagine, what the word was that I 

 suggested as more logical than ' paradox.' 



